1. Field of Invention
Aspects of the invention can relate to gray scale correction processing of image data. More specifically, the invention can relate to gray scale correction processing, such as color correction or gamma (γ) correction based on lookup tables (LUTs).
2. Description of Related Art
Related art gamma correction processing is processing for adjusting display characteristics of image data in accordance with characteristics of a display device, such as a CRT or an LCD in an image display apparatus for displaying image data. Generally, gamma correction processing can be carried out using, for example, an LUT storing gamma characteristics data (gray scale correction characteristics data) created on the basis of the display characteristics of a display device. Gamma characteristics define relationship between input gray scale values and output gray scale values. The image display apparatus obtains output gray scale values corresponding to input gray scale values of input image data by referring to the gamma characteristics, and displays an image corresponding to the image data on a display device according to the output gray scale values.
Also, when the image display apparatus performs color correction on input image data to achieve desired color characteristics for display, an LUT storing color conversion characteristics prepared in advance is used. An example of such related art color correction and gamma correction is disclosed in Japanese Unexamined Patent Application Publication No. 9-271036.
With the recent improvement in picture quality in cellular phones and other electronic apparatuses, the capacity of a storage device, such as a RAM needed to implement an LUT for gray scale correction characteristics data increases as the number of gray scale levels of image data increases. In view of this, a method has been proposed in which gray scale correction characteristics data for a number of gray scale levels smaller than the number of gray scale levels of input image data is stored in an LUT and gray scale correction characteristics data for the insufficiency is interpolated by linear approximation or the like. (Refer to, for example, PCT Japanese Translation Patent Publication No. 2002-534007).
In order to interpolate gray scale correction characteristics data by linear approximation or the like, output gray scale values of two endpoints of a portion to be interpolated are needed, so that reading operation must be executed twice with an LUT storing a single set of gray scale correction characteristics data. Thus, power consumption increases due to the increased number of times of reading operation, and a clock rate higher than a normal clock rate is required.